DittoBox: You haven't played any of the Halo games on Legendary and/or with the Mythic skull, have you? One of the hardest games I've ever played with that stuff on. :)
Rohan15: I have, not as hard as you say it is.
I agree. I haven't played Halo 3, but Halo 1 and 2 on legendary really aren't terribly hard, even if you try the silly things I like to do (e.g. keeping all my suicidal marines alive). Admittedly, it made a lot more difference in Halo 2, and made the game both challenging and a lot better . . . but it was entirely doable, even though I'm awful at using console controllers.
That said, many parts of Far Cry aren't all that difficult no matter what the level, but the ability of normal enemies to pose a real challenge in the right tactical landscape does give it a different feel. Between Far Cry's hard parts with mouse and keyboard and Halo 2's with controllers, I'm not sure which is harder [it's been a while] . . . but if I had mouse+keyboard for Halo 2, I don't think there'd be much question.
Still, I read his original comment not as a reference to difficulty so much as a statement of the simple fact that you do have to play quite *differently* - one glaringly obvious reason is that in Halo, you can strategically take a few hits over and over so long as you have time to recharge your shield; this enables tanking in some situations if you're a good shot and skilled at finding cover on the fly. Far Cry has no such option, and on realistic you can't afford to take many hits at all. The two games are designed for and require very different play-styles. (I do tend to play everything in a sniper-focused way, but Halo lets me do that on the run, among other things.)
Edit:
on reflection, I'm pretty sure the hardest parts of Halo 2 took me more time to beat, but I really do put a lot of that down to my complete lack of controller skills; much of the time I died because I failed to get off or misplaced a critical shot. Given how ridiculously much easier I found Halo 1 on the PC than on the console, I strongly suspect that the toughest Halo 2 battles would be less problematic than a couple painful fights from Far Cry.